The invention relates to a measuring instrument and more specifically to an instrument for measuring the density or modulus of material that has been subjected to compression forces.
All earth materials possess specific discrete strength and compression characteristics that must be defined in order to design structures to be supported on those materials. These various characteristics are referred to as the soil's “Engineering Properties.” One of these properties is the soil “modulus,” which relates deformation of the soil to an applied load that causes the deformation. Modulus is a very significant engineering property for designing floor slabs on-grade and footings, and for estimating settlements.
Engineering properties of soils can be determined by means of special field and/or laboratory tests. Laboratory tests are often of questionable value due to the inability of the engineer to obtain a truly “undisturbed” sample of the soil for the test. Additionally, most field tests for engineering properties (including modulus:) are labor intensive and require significant time to conduct. Nonetheless designs for pavements, slabs on-grade, and foundations using subgrade modulus were developed and widely used in the 19th and 20th centuries by the Civil Aeronautical Administration (CCA, now known as the Federal Aviation Administration) and the U.S. Navy.
Since engineering properties tests are typically relatively slow and costly, a number of faster and less costly “Index Tests” have been developed over the years which enable the designer to estimate the engineering properties he needs based on correlations with various index test results. Typical index tests include moisture content, density, various penetration tests, and others. Due to the variations in soils in nature, and inherent difficulties in correlating index test results to soil type, the estimation of a modulus value for a given soil based on index tests can result in a crude approximation at best. Hence, designs based either primarily or solely on estimating modulus from index tests must include relatively large factors of safety in order to, hopefully, account for errors in the correlations.
With the advent of the nuclear densometer (a rapid, in-place density testing device), the practice of evaluating subgrade modulus in the field by direct measurement (i.e., by means of a time consuming plate load test) was replaced almost exclusively by correlation with in-place density. Additional developments in field penetration testing (the Cone Penetration Test and standard Penetration Test), which are also index tests, further reduced the determination of soil modulus by direct measurement in the field. In response, other field tests have been developed to measure soil modulus in the field (i.e., pressure meter and dilatometer); however, these tests employ a horizontal force applied to the soil within a borehole, and the modulus corresponding to a vertically applied force is inferred by means of soil mechanics principles. Since the design of pavements, slabs on-grade and foundations rely on the soil modulus resulting from a vertically applied load, these more recent field tests still provide only an indication of the appropriate modulus for design. Further, the pressure meter and dilatometer tests are time consuming and costly.
Now, as a result of the development of this displacement instrument it is possible to directly, accurately and economically measure the soil modulus in-place, and in the vertical direction. By so doing, design and construction cost savings could be realized by further minimizing necessary soil testing and by potentially reducing the factors of safety applied in conventional engineering design. Specific applications could include establishing design modulus values in the field during soils investigations, confirming selected design modulus values during preconstruction site grading and confirming the modulus improvement achieved by various sub-grade stabilization/reenforcement techniques.
It is an object of the invention to provide a novel displacement instrument that overcomes an existing problem of not being able to measure the modulus or density of the aggregate piers produced by the method disclosed in U.S. Pat. No. 6,453,766.
It is another object of the invention to provide a novel displacement instrument that allows each of the lifts of approximately 12-18 inches of aggregate that is tamped into a pier forming hole to be tested at that time for its density or modulus. These pier holes are often up to 35 feet deep or deeper.
It is also an object of the invention to provide a novel displacement instrument that will allow aggregate piers to be constructed having a density or modulus that is consistent from the bottom of the hole to its top.
It is an additional object of the invention to provide a novel displacement instrument that can be mounted on the side of a hydraulic breaker mounted on the front end of the boom of a crane.
It is a further object of the invention to provide a novel displacement instrument that can withstand the constant repetitive strokes of the tamper plate striking the aggregate at a force of 15,000 psi or greater.
It is another object of the invention to provide a novel displacement instrument that is portable so that it can be removed from any hydraulic breaker when not in use or installed on another hydraulic breaker.
It is also an object of the invention to provide a novel displacement instrument having a free floating circuit board with an air pressure transducer mounted thereon.